1. Field of the Invention
The invention relates to methods of inhibiting tumor cell proliferation by inhibiting FoxM1B activity. Specifically, the invention relates to methods and compositions for inhibiting tumor cell proliferation by inhibiting FoxM1B activity, expression, or nuclear localization in a tumor cell.
2. Background of the Related Art
The Forkhead box transcription factors have been implicated in regulating cellular longevity and proliferative capacity. Such studies include a finding of increased longevity in C. elegans bearing a mutant daf-2 gene, which encodes the worm homolog of the insulin/Insulin-like Growth Factor 1 (IGF1) receptor (Lin et al., 1997, Science 278: 1319-1322; Ogg et al., 1997, Nature 389: 994-999). Disruption of the daf-2 gene abolishes insulin-mediated activation of the phosphatidylinositol 3-kinase (PI3K)-protein kinase B/Akt (Akt) signal transduction pathway and prevents inhibition of the forkhead transcription factor daf-16 (corresponding to mammalian homologs FoxO1 or Fkhr) (Paradis and Ruvkun, 1998, Genes Dev. 12: 2488-2498). Activation of the PI3K/Akt pathway phosphorylates the C-terminus of the Daf-16 (FoxO1; Fkhr) gene product and mediates its nuclear export into the cytoplasm, thus preventing FoxO1 transcriptional activation of target genes (Biggs et al., 1999, Proc. Natl. Acad. Sci. USA 96: 7421-7426; Brunet et al., 1999, Cell 96: 857-68; Guo et al., 1999, J. Biol. Chem. 274: 17184-17192).
Studies of Daf-2− C. elegans mutants have demonstrated that Daf-16 stimulates expression of genes that limit oxidative stress (Barsyte et al., 2001, FASEB J. 15: 627-634; Honda et al., 1999, FASEB J. 13: 1385-1393; Wolkow et al., 2000, Science 290: 147-150) and that the mammalian FoxO1 gene could functionally replace the Daf-16 gene in C. elegans (Lee et al., 2001, Curr. Biol. 11: 1950-1957). In proliferating mammalian cells, the PI3K/Akt signal transduction pathway is essential for G1 to S-phase progression because it prevents transcriptional activity of the FoxO1 and FoxO3 proteins, which stimulate expression of the CDK inhibitor p27kip1 gene (Medema et al., 2000, Nature 404: 782-787). Moreover, genetic studies in budding yeast demonstrated that forkhead Fkh1 and Fkh2 proteins are components of a transcription factor complex that regulates expression of genes critical for progression into mitosis (Hollenhorst et al., 2001, Genes Dev. 15: 2445-2456; Koranda et al., 2000, Nature 406: 94-98; Kumar et al., 2000, Curr. Biol. 10: 896-906; Pic et al., 2000, EMBO J. 19: 3750-3761).
Forkhead Box M1B (FoxM1B) transcription factor (also known as Trident and HFH-11B) is a proliferation-specific transcription factor that shares 39% amino acid homology with the HNF-3 winged helix DNA binding domain. The molecule also contains a potent C-terminal transcriptional activation domain that possesses several phosphorylation sites for M-phase specific kinases as well as PEST sequences that mediate rapid protein degradation (Korver et al., 1997, Nucleic Acids Res. 25: 1715-1719; Korver et al., 1997, Genomics 46: 435-442; Yao et al., 1997, J. Biol. Chem. 272: 19827-19836; Ye et al., 1997, Mol. Cell Biol. 17: 1626-1641).
In situ hybridization studies have shown that FoxM1B is expressed in embryonic liver, intestine, lung, and renal pelvis (Ye et al., 1997, Mol. Cell Biol. 17: 1626-1641). In adult tissue, however, FoxM1B is not expressed in postmitotic, differentiated cells of the liver and lung, although it is expressed in proliferating cells of the thymus, testis, small intestine, and colon (Id). FoxM1B expression is reactivated in the liver prior to hepatocyte DNA replication following regeneration induced by partial hepatectomy (Id).
FoxM1B is expressed in several tumor-derived epithelial cell lines and its expression is induced by serum prior to the G1/S transition (Korver et al., 1997, Nucleic Acids Res. 25: 1715-1719; Korver et al., 1997, Genomics 46: 435-442; Yao et al., 1997, J. Biol. Chem. 272: 19827-19836; Ye et al., 1997, Mol. Cell Biol. 17: 1626-1641). Consistent with the role of FoxM1B in cell cycle progression, elevated FoxM1B levels are found in numerous actively-proliferating tumor cell lines (Korver et al., 1997, Nucleic Acids Res. 25: 1715-1719; Yao et al., 1997, J. Biol. Chem. 272: 19827-36; Ye et al., 1997, Mol. Cell Biol. 17: 1626-1641). Increased nuclear staining of FoxM1B was also found in human basal cell carcinomas (Teh et al., 2002, Cancer Res. 62: 4773-80), suggesting that FoxM1B is required for cellular proliferation in human cancers.
FOXM1B facilitates development of cancers in several ways. First, it transcriptionally activates genes involved in cell-proliferation, and promotes progression through G1-S and G2-M phases of the cell cycle (Wang, et al., 2005, Mol Cell Biol, 25: 10875-10894; Laoukili et al., 2005, Nat Cell Biol. 7: 126-136). It stimulates expression of DNA repair genes, ensuring chromosome stability (Tan et al., 2007, Mol Cell Biol. 27: 1007-1016; Wonsey & Follettie, 2005, Cancer Res. 65: 5181-5189). In addition, FoxM1 has been implicated in alleviating oxidative stress in tumor cells by activating ROS scavenger proteins (Park et al., 2009, Embo J. 28: 2908-2918) and mediating resistance to Herceptin and paclitaxel (Carr et al., 2010, Cancer Res, 70: 5054-5063; Kwok, et al., 2010, Mol Cancer Res, 8: 24-34). One study in a mouse hepatocellular carcinoma (HCC) model demonstrated that FOXM1 also functions as a potent activator of tumor metastasis through promoting the epithelial-to-mesenchymal transition (EMT), increased motility of the tumor cells, and establishment of pre-metastatic niches in the distal target organ (Park et al., 2011, EMBO Mol Med, 3: 21-34; Raychaudhuri & Park, 2011, Cancer Res. 71: 4329-4333). Two studies in neuroblastoma and embryonic carcinoma cells indicated a role of FOXM1 in the maintenance of the undifferentiated state of the tumor cells by activating pluripotency-associated genes (Wang et al., 2011, Cancer Res, 71: 4292-4302; Xie et al., 2010, Nucleic Acids Res. 38: 8027-8038).
FOXM1 is a proliferative-specific transcriptional factor whose expression is unique to the proliferating cells (Korver et al., 1997, Nucleic Acids Res, 25: 1715-1719; Ye et al., 1999, Mol Cell Biol, 19: 8570-8580). Several strategies have been developed to target FoxM1 in cancer cells. Based on the fact that FoxM1 is an inhibitory target of mouse ARF tumor suppressor, a cell penetrating ARF 26-44 peptide which consists of 9 N-terminal D-arginine (D69 Arg) residues and amino acid residues 26-44 of the mouse ARF protein was synthesized (Kalinichenko et al., Genes Dev. 2004, 18: 830-850). The ARF 26-44 peptide, which inhibits FOXM1 by sequestering it to the nucleolus, was effective in diminishing tumor size in HCC by reducing tumor cell proliferation and inducing apoptosis (Gusarova et al., 2007, J Clin Invest, 117: 99-111). That ARF peptide also effectively prevented pulmonary metastasis of HCC cells (Park et al., 2011, EMBO Mol Med. 3: 21-34). In addition, thiazole antibiotics have been shown to down-regulate FOXM1 and induce apoptosis in various cancer cells (Bhat et al., 2009, PLoS One, 4: e5592; Radhakrishnan et al., 2006, Cancer Res, 66: 9731-9735).